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Gravity gradiometer based on ultra-cold rubidium atoms
Gravity gradiometer based on ultra-cold rubidium atoms
Paris Observatory - SYRTE
CAD of the instrument. The two trapping chambers, with their 2D MOT, link by a tube.
Cold atom gravity gradiometers perform gravity measurements simultaneously on two spatially separated atomic clouds. The differential measurement gives the local gravity gradient, while rejecting common-mode parasitic vibrations.
In order to reach a high sensitivity, the instrument is made of two trapping chambers separated by 1 m, where ultra-cold atoms will be generated, launched by moving lattice and then interrogated with LMT (large momentum transfer). The atoms are loaded from a 2D MOT (two-dimensional magneto-optical trap) to a 3D mMOT (mirror-MOT), the reflective surface of the mMOT is an atom chip that will then be used to cool down the atoms to ultra-low temperature.
While waiting to have two trapping chambers with atom-chips, I built a single one with a 2D MOT, a detection chamber, a launching tube and a dielectric mirror instead of an atom chip for the mMOT. I also built a phase locked Bloch elevator laser system, to be able to generate a moving lattice and launch the atoms. With this configuration, a first cloud is generated in the trapping chamber and then vertically launched. Right after, a second cold atoms cloud is generated in the same chamber, and released when the first cloud is at the apogee of its trajectory. Both clouds are then interrogated with the same laser beam.
By turning off the isolation platform, we can use the ground vibrations to scan the interferometric phase. The vibration signal is measured by a seismometer and its effect on the interferometric phase was characterised. This correlation allows to extract the phase of each interferometer and readout the gravity gradient.
The results were published in Phys. Rev. A 96, 053624 (2017).
Trapping chamber with the collimators and coils. Above it, the tube where the atom are launched. The detection chamber is placed under the trapping chamber
Sequence use to perform gravity gradient measurements with a single source of atoms.
Allan standard deviations of the seismic phase, the two individual interferometric phase and the gradiometric phase.
Compact gravity gradiometer
Compact gravity gradiometer
University of Birmingham - Shool of Physics and Astronomy
To push the industrial transfer of quantum sensor, the instruments have to have a high technology readiness level. To do so, reduce the size, weight and power consumption (SWaP) is an important step.
Moreover, gravity gradiometer is a dedicated instrument for field measurement, due to its capability to cancel some vibration noises. Develop quantum gravity gradimeter with a low SWaP is a key point to the industrial transfer.
I designed this experiment with a single trapping chamber, where a single cloud will be split in two and each part is launched in opposite direction using Bloch elevator. All the steps, cooling, launching, Raman interrogation and detection, are generated by a single arm fibred laser bench. The full experiment can be lift by a drone.
More information after the publication of the patents.
Talk about quantum gravity gradiometer.
Transportable gravity gradiometer
Transportable gravity gradiometer
University of Birmingham - Shool of Physics and Astronomy
While gravity cartography can be limited in resolving features on the meter scale due to the long measurement times required to remove vibrational noise. Gravity gradiometry overcomes this limitation and suppresses the effects of micro-seismic and laser noise, thermal and magnetic field variations, and instrument tilt.
The removal of vibrational noise enables improvements in instrument performance to directly translate into reduced measurement time in mapping. The sensor parameters are compatible with applications in mapping aquifers, determining soil properties and water content, archaeology, and reducing the risk of unforeseen ground conditions in the construction of critical energy, transport, and utilities infrastructure. This new tool provides a new window into the underground and has implications for various industries, including geophysics, engineering, and climate research.
The instrument we developped achieves a statistical uncertainty of 20 E and was used to perform a 0.5 m spatial resolution survey across an 8.5 m long line, detecting a 2-meter tunnel.
The results were published in Nature 602, 590–594 (2022).
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